1. Field of the Invention
The present invention relates to a damper device for damping vibrations transmitted from one to the other of a support element and a suspended element when a heavy element as a source of such vibrations is supported on the support element or when such element is supported on and fixed by the support element to which external vibrations are apt to be transmitted. The damper device of the present invention is suitably adapted for supporting and fixing an engine to a body or a frame of a vehicle.
2. Description of the Prior Art
In a damper device, in particular, in a damper device to be used in an engine suspension of a vehicle, a thick, elastic member such as a rubber block is normally used. However, such a block generally has high flexibility and elasticity. For this reason, the block cannot always provide a good damper effect against vibrations of frequencies and magnitudes of vibration within wide ranges.
A conventional damper device is disclosed in U.S. Pat. No. 4,159,091, DE Pat. No. 2,727,244. In this device, a sealed space is defined by a rubber block and two frame plates. The sealed space is partitioned into two chambers by a partition wall which is fixed to one frame plate and which has a movable member and an orifice formed therein. A liquid is filled in the sealed space to a level such that at least the partition wall is immersed in the liquid. When vibrations are transmitted to the block, if such originated from an engine in operation and have a high frequency and a very small magnitude of vibration, a change in volume in one chamber upon deformation of the rubber block is compensated for by displacement of the movable member in the partition wall and stiffness of the rubber block is kept very low. On the other hand, if the vibrations transmitted to the rubber block are of a low frequency and a large magnitude, such as cranking vibrations of an engine, a change in volume of one chamber is used to cause the liquid to flow from the one chamber into the other chamber through the orifice formed in the partition wall, and stiffness of the rubber block is significantly increased by liquid flow resistance through the orifice.
In the above-mentioned damper device, in order to damp vibrations having a magnitude of vibration exceeding 0.5 mm, the liquid is allowed to flow from one chamber to the other chamber through the orifice formed in the partition wall, and the flow resistance obtained upon liquid flow is utilized to provide a damper effect. However, the orifice is formed in the movable member comprising a thin plate of a rigid material such as metal or an elastic material such as rubber. Alternatively, the orifice is defined by a gap between a circular hole formed in the movable member and a pin inserted into the circular hole and fixed to the rubber block or blocks. Since the flow resistance of the liquid flowing through the orifice is determined by the effective passage cross-sectional area of the orifice and its length, if an orifice is formed in a thin plate, the effective cross-sectional area must be accurately set since the length of the passage is limited by the thickness of the thin plate. If an orifice is defined by a gap between a circular hole and a pin, a high machining accuracy of the circular hole in the movable member and the outer circumferential surface of the pin is necessary. In addition, when the movable member and the pin slide against each other, the effective passage cross-sectional area changes due to wear. For this reason, it is difficult to correctly set the flow resistance of the liquid through the orifice, and machining and assembly of respective components require high precision.